Pressure-induced semiconductor-metal transitions in amorphous Si and Ge

A pressure-induced semiconductor-metal transition accompanied by a sharp resistance drop with a factor of approximately 10–6 has been found for amorphous Si at 100 kbar and amorphous Ge at 60 kbar. The transition in Si is a reversible process between amorphous semiconductor and amorphous metal, while that in Ge is an irreversible process with crystallization into a diamond-type structure. The pressure-induced metallic character in amorphous Si and Ge has been demonstrated by superconductivity at low temperatures. The metallic conduction is believed to be due to structural modifications which remain amorphous.